The long term objectives of this project are to define mechanisms of tumor-induced immune suppression of macrophage function. Macrophages are a critical component of anti- tumor immunity but may be subverted from the classically-activated, or M1 phenotype, which mediates tumor elimination, to an alternatively-activated, M2 phenotype, which promotes tumor progression. Interleukin-4 (IL-4) signaling through its receptor, IL-4R-a, is a pivotal regulator of macrophage polarization to the M2 phenotype. Disruption of IL-4 signaling may therefore represent a useful strategy to attenuate the subversion of tumor immunity mediated by M2 tumor- associated macrophages. Our general strategy is to define the phenotypic characteristics of tumor macrophages from patients with non-Hodgkin's lymphoma who participate in a phase I immunotherapy trial involving the administration of anti-CD20 antibody into the cerebrospinal fluid in patients with recurrent disease in the brain. In addition, we will use genetic and pharmacologic strategies in mouse models to dissect the effect of cytokine signaling on tumor angiogenesis, macrophage phenotype and immunotherapeutic response in a model of CNS lymphoma. The specific aims are to define the relationship between IL-4 signaling, macrophage differentiation, lymphoma growth and response to anti-CD20 antibody. We envision five goals: (1) Define subpopulations of tumor macrophages within the CSF and their relationship to IL-4-induced programming, (2) Define the relationship between macrophage polarization to the M2 phenotype and resistance to anti-CD20 antibody, (3) Define the relevant cytokines and chemokines which predict this resistance, (4) Evaluate the relationship between IL-4 expression by tumor vessels, M2 macrophage programming and tumor growth, (5) Determine the impact of defects in cytokine signaling on macrophage polarization and response to anti-CD20 antibody. Results of these studies will have implications for a variety of disorders and cancers in which immune surveillance as well as antibody-dependent cell-mediated cytotoxicity are important means of disease control. These studies may lead to the development of new therapies which modulate macrophage programming and potentiate their anti-tumor potency.